The present invention relates to thermally responsive valves for thermostats intended for use in controlling flow of coolant in an internal combustion engine. In particular, the present invention relates to thermostats in engines operated under fully loaded conditions and which may at times be subject to overheating.
Engine thermostats or thermally responsive coolant flow control valves typically employ a thermally responsive element which utilizes thermally expansible wax in a cup which is sealed by a rubber diaphragm and rubber plug. Upon expansion of the wax at a critical temperature, the volume of the wax increases dramatically and the diaphragm forces the plug to act against an output member which opens the poppet or valve member of the thermostat which is initially closed against an annular valve seat.
When thermostats employing such a thermally expansible wax filled power element for the thermal sensor are exposed to overtemperatures on the order of 400.degree. Fahrenheit, the extreme expansion of the wax material causes the piston to pop out of the guide or bind, and also causes the spring retainer to block adequate flow of coolant, and thus the thermostat fails in service.
Accordingly, it has been desired to provide a way or means of preventing excessive movement of the operating member of a expansible wax powered engine coolant thermostat upon exposure to overtemperature in a manner which is simple and low in manufacturing cost and requires minimum redesign and/or tooling changes in currently mass-produced thermostats.